1. Field of the Invention
The present invention relates to a process for producing L-amino acids by fermentation and microorganisms for producing L-amino acids.
2. Discussion of the Background
L-amino acids have been widely used as seasonings, medical drugs, feed additives, chemicals, reagents and the like. L-amino acids, which are produced by fermentation on an industrial scale, include L-glutamic acid, L-lysine, L-glutamine, L-arginine, L-phenylalanine, L-alanine, L-threonine, L-isoleucine, L-histidine, L-proline, L-valine, L-serine, L-ornithine, L-citrulline, L-tyrosine, L-tryptophan and L-leucine, etc. As microorganisms utilized for the production of L-amino acids, there are those belonging to the genus Brevibacterium, the genus Corynebacterium, the genus Bacillus, the genus Escherichia, the genus Seratia, the genus Providencia, and the genus Arthorbacter, etc.
It is important to produce L-amino acids at low costs on an industrial scale by enhancing the fermentation yield and accumulation of L-amino acids. To produce L-amino acids industrially at low costs utilizing these various microorganisms, improved breeding of microorganisms has often been used. That is, the L-amino acid production of wild strains per se is extremely poor in many instances, and therefore, methods for imparting nutrient auxotrophy, imparting analog resistance or imparting nutrient auxotrophy in combination with analog resistance, through artificial mutation; or potentiating a gene for amino acid biosynthesis, etc. by genetic recombination, and the like are used to increase the L-amino acid productivity of the wild strain. However, fermentation with conventional strains does not produce L-amino acids in a sufficiently high yield.
Thus, there remains a need for a process which will produce L-amino acids by fermentation in high yield. There also remains a need for microorganisms which produce L-amino acids in high yield.